The present invention relates to a resist composition suitable for the production of printed circuit boards. More particularly, the present invention relates to a resist composition having excellent reliability in heat resistance, adhesion to copper, electrical characteristics, fire retardance and impact resistance. The resist composition is particularly useful as a photosolder resist.
With the recent reduction in the size of electronic apparatus and increase in the number of functions thereof, the trend of printed circuit boards is toward higher density. For example, it has been considered to produce a multi-chip module having a plurality of bare chips or chip size packages mounted on a resin substrate base, which is excellent in mass producibility, instead of on the conventional base, i.e., a device base or a ceramic base. In order to produce such a high density mounting board, a resist, particularly a photosolder resist, excellent in resolution, heat resistance, reliability, workability, etc. is required.
As a photosolder resist there is disclosed in JP-A-61-243869 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) a photosetting and thermosetting liquid resist ink composition, which can be developed with an alkaline solution. The composition comprises: (A) an active energy ray-curing resin obtained by the reaction of: a reaction product of a novolak epoxy compound and an unsaturated monocarboxylic acid; and a saturated or unsaturated polybasic acid anhydride; (B) a photopolymerization initiator; (C) a diluent; and (D) a thermosetting component comprising an epoxy compound having two or more epoxy groups per molecule.
The cured product of such a composition is excellent in hardness as a solder resist but exhibits a deteriorated flexibility. Therefore, when such a composition is applied, in the form of liquid resist to form a solder resist, onto a printed circuit board which is thin for accomplishing high density wiring, the resulting cured solder resist may crack due to warpage, twist or impact developed upon mounting. When cracking occurs, it causes several troubles. For example, solder may be attached to undesirable areas during soldering. Further, moisture absorption due to the cracking may cause corrosion of a conductor or a decrease of the insulating property between conductors.
The active energy ray-curing resin having carboxylic acid and the epoxy resin constituting the liquid resist readily react with each other and thus they are usually used in the form of a two-liquid type resist. In other words, when a liquid resist is formed on a printed circuit board, for example, by screen-printing, two components need to be mixed immediately before use. It is also disadvantageous in that available pot life is limited, resulting in a deteriorated workability. Various one-liquid type photosolder resists developable with an alkaline solution have also been studied. However, no photosolder resists excellent both in crack resistance and adhesion to copper have been obtained.
The inventors made studies of a composition capable of preventing the above-mentioned cracking of a photosolder resist and a method for imparting a good adhesion between the resin layer and copper.
Accordingly, an object of the present invention is to provide a resist composition, which can be developed with an alkaline aqueous solution, which has satisfactory impact resistance and heat resistance as well as satisfactory reliability in electrical insulating properties, etc., and which further provides excellent workability.
Another object of the present invention is to provide a solder resist formed from the resist composition and a printed circuit board having the solder resist.
Other objects and effects of the present invention will become apparent from the following description.
The above-described objects of the present invention have been achieved by providing:
1. A resist composition comprising:
a curable composition mainly comprising (1) at least one of an alkali-soluble acrylic compound and an alkali-soluble methacrylic compound;
(2) a fine-particulate crosslinked elastic polymer having a carboxyl group; and
(3) an agent for enhancing adhesion with respect to copper.
The terms xe2x80x9cat least one of acrylic compound and methacrylic compoundxe2x80x9d are hereinafter referred to as xe2x80x9c(meth)acrylic compoundxe2x80x9d.
Component (2) is a component for mainly rendering the resist flexible. Component (3) is a component for enhancing adhesion to copper. An inorganic filler, a fire retardant, a pigment, etc. may be appropriately added to the resist composition according to the present invention.
The present invention is also directed to the following embodiments:
2. The resist composition according to the above item 1, wherein said adhesion-enhancing agent (3) is at least one of a carboxyl benzotriazole and a phosphoric acid acrylate.
3. The resist composition according to the above item 1 or 2, wherein said curable composition is a curable composition (A) which comprises:
(A1) at least one of an alkali-soluble acrylic compound and an alkali-soluble methacrylic compound, each having a carboxyl group;
(A2) a polymerizable compound having one or more Cxe2x95x90C unsaturated double bonds;
(A3) an ultraviolet-ray polymerization initiator for said polymerizable compound (A2); and
(A4) a thermal polymerization initiator for said polymerizable compound (A2).
4. The resist composition according to the above item 3, further comprising a sensitizer for ultraviolet-ray polymerization.
5. The resist composition according to any one of the above items 1 to 4, wherein said at least one alkali-soluble (meth)acrylic compound (1) has a carboxyl group.
6. The resist composition according to the above item 5, wherein said at least one alkali-soluble (meth)acrylic compound (1) is a reaction product of:
a reaction product of an epoxy compound and an unsaturated monocarboxylic acid; and
a polybasic acid anhydride.
7. The resist composition according to the above item 6, wherein said at least one alkali-soluble (meth)acrylic compound (1) is a carboxyl group-containing compound obtained by the reaction of at least one epoxy (meth)acrylate with a polybasic acid anhydride.
8. The resist composition according to the above item 1, wherein said adhesion-enhancing agent (3) is a thermosetting component comprising an epoxy compound containing at least two epoxy groups per molecule.
9. The resist composition according to the above item 8, wherein said curable composition is a curable composition (B) which comprises:
(B1) a reaction product of:
a reaction product of an epoxy compound and an unsaturated monocarboxylic acid; and
a polybasic acid anhydride;
(B2) an ultraviolet-ray polymerization initiator; and
(B3) a volatile organic solvent.
10. A solder resist formed from a resist composition according to any one of the above items 1 to 9.
11. A solder resist film obtained by forming a resist composition according to any one of the above items 1 to 9 into sheet.
12. A printed circuit board having thereon a solder resist formed from a resist composition according to any one of the above items 1 to 9.
The resist composition according to the above item 3, i.e., comprising a curable composition (A) is hereinafter referred to as a xe2x80x9cresist composition (A)xe2x80x9d. Having such an arrangement, the resist composition (A) has ultraviolet-ray curing property.
The resist composition according to the above item 9, i.e., comprising a curable composition (B) and containing the specific adhesion-enhancing agent (3) as defined in the above item 8 is hereinafter referred to as a xe2x80x9cresist composition (B)xe2x80x9d.
Component (A1) constituting the resist composition (A) is a base material for mainly rendering the resist composition soluble in an alkaline solution. Components (A2) and (A3) each are a component for crosslinking the resist when irradiated with ultraviolet rays. Component (A4) is a component for thermally curing and reinforcing the resist.
Component (B1) constituting the resist composition (B) is a base material for rendering the resist composition soluble in an alkaline solution. Component (B2) is a component for crosslinking the resist when irradiated with an active energy ray such as ultraviolet ray. Component (B3) is an organic solvent for coating the resist composition.
The resist composition (A) according to the present invention can be applied onto a film and then dried to give a dry film type resist. Alternatively, the resist composition (A) can also be used as a liquid resist. Specifically, the resist composition (A) is applied onto a printed circuit board by a screen printing method, a curtain coating method or a roll coating method, irradiated with an active energy ray so as to cure necessary areas, followed by dissolving the unexposed areas away with a weakly alkaline aqueous solution to form a resist-patterned film. By thermally curing the resist-patterned film, a permanent film having a high flexibility and high heat resistance can be obtained.
On the other hand, the resist composition (B) is mainly used as a liquid resist. In other words, the epoxy group in the specific adhesion-enhancing agent (3) and the free carboxyl group present in the side chain of component (B1) undergo copolymerization reaction to provide a coating film having excellent properties such as high heat resistance, solvent resistance, plating resistance, adhesion to copper foil, electrical properties and hardness. In addition, the incorporation of the fine-particulate elastic polymer having a carboxyl group as component (2) makes it possible to obtain a resist composition which can hardly crack due to stress such as thermal shock, mechanical impact, warpage and twist. If the fine-particulate polymer is merely elastic, the resulting resist composition on unexposed areas after exposure and development is unwilling to be dissolved away. Therefore, the fine-particulate elastic polymer having a carboxyl group is used.